Origins for inflation

I will review the particle theory origin of inflation for generating large scale structures and the observed temperature anisotropy in the cosmic microwave background (CMB) radiation. Since inflaton energy density creates all matter, it is important to understand the process of reheating and preheating into the relevant degrees of freedom required for the success of Big Bang Nucleosynthesis. We discuss two distinct classes of models, one where inflaton belongs to the hidden sector, which couples to the Standard Model gauge sector very weakly. There is another class of models of
inflaton and curvaton, which are embedded within Minimal Supersymmetric Standard Model (MSSM) gauge group and beyond, and whose origins lie within gauge invariant combinations of supersymmetric quarks and leptons. Their masses and couplings are all well motivated from low energy physics, therefore such models provide us with a unique opportunity that they can be verified/falsified by the CMB data and also by the collider and non-collider based experiments. I will briefly discuss stringy origin of inflation, alternative cosmological scenarios, and bouncing universes.